1. Technical Field
The present invention relates generally to computer-implemented data hiding, and more particularly, to computer-implemented audio data hiding.
2. Background and Summary of the Invention
Electronic media distribution imposes high demand on content protection mechanisms for secure distribution of media. Imperceptible data hiding for copy control and copyright protection of digital media is gradually gaining widespread attention due mainly to the prominence of electronic media distribution via the Internet.
In particular, the ease with which digital data can be transmitted over the Internet, and the fact that unlimited perfect copies of the original can be made and distributed, are the major causes of concern for intellectual property rights management. Copyright protection and playback/record control need to be addressed so that content owners will agree to electronic distribution of digital media. The problem is amplified by the fact that digital copy technology, such as DVD-RAM, CD-R, CD-RW, and DTV, and high quality compression and digital multimedia signal processing software are widely available. For example, the availability of MP3 compression (MPEG-I layer-3 audio coding standard) makes CD (compact disc) quality music available to users through downloads from unauthorized web sites on the Internet.
Previous approaches of data hiding in audio media have concentrated on embedding hidden data in the base domain (original time domain). These approaches lend themselves to attacks and distortions on the synchronization structure of the audio signal. Such kind of attacks and distortions (for example, time-scale warping and pitch-shift warping attacks) can substantially change the structure of audio signal in the time domain but with little affect on the audio quality. Thus, they are commonly seen as the most challenging problems in audio data hiding.
The present invention aims at overcoming the aforementioned disadvantages. The present invention embeds the hidden data in the transform domain, preferably, cepstrum or Linear Prediction residue domain. In accordance with the teachings of the present invention is a computer-implemented method and apparatus for embedding hidden data in an audio signal. An audio signal is received in a base domain. The received audio signal is transformed to a non-base domain. The hidden data is embedded in the transformed non-base domain audio signal. The transform-domain representation can be shown to be more robust to severe synchronization destructive attacks than base domain representation. For instance, perceptually important features of an audio signal, such as pitch or vocal track, can be well parameterized in certain transform domain. Common signal processing attacks seldom modify those features unless paying the penalty on the transparency requirement, i.e., introducing significant degradation on the audio perceptual quality.
In transform domain, the present invention employs Statistical Mean Manipulation embedding strategy. This is based on the observation that statistical mean of selected transform coefficients typically experience small variation after most common signal processing. Hidden data, in binary format, is embedded into the audio on a frame-by-frame basis by manipulating the statistical mean. A positive mean (larger than certain preset threshold) is enforced to carry bit “1”. The introduced distortion is controlled by psychoacoustic model to meet transparency requirements. In addition, the security level of the scheme can be further increased via a scrambling technique on the transform coefficients with the scrambling filter kept as a secret key by the content owner. With these novel techniques, the present invention maximizes the survivability of embedded data under the condition of meeting the requirement of transparency (which is that the embedded data should not introduce any significant audible distortion).